The present invention relates to a method and apparatus for fracturing rock or similar material, in a way so as to achieve removal of large pieces of such material.
A conventional method of breaking rock is to drill into the rock and set explosive charges to blast away sections of rock. Aside from the noise, flying rock fragments and debris the drill-and-blast technique is somewhat unpredictable and frequently entails extra cost. Another technique is that of coring which involves drilling a hole in the shape of a cylindrical sleeve and then inserting tools into the sleeve-like opening and by impacting the tools attempting to fracture the central core of solid material. Unfortunately, it is common for the tools to become jammed in the hole or, for the core to break into many small pieces so that removal of the pieces becomes time consuming and inconvenient.
U.S. Pat. No. 99,595 issued Feb. 8, 1870 to Robb discloses a technique of filling a drilled hole with water or other liquids, and then inserting a plunger fitted to work as tightly as possible above the water, and subjecting the plunger to impact forces such as by a hammer blow. The pressure transmission through the liquid imparts force over the side wall and causes fracturing. There is a practical limitation of the latter method due to the need to seal the water at the side wall between the plunger and the hole. Any leaks reduce substantially the pressure developed in the liquid.
U.S. Pat. No. 3,988,037 issued Oct. 26, 1976 discloses a method similar to Robb in that a pre-drilled hole is filled with hydraulic fluid. A piston is then driven into the hole at speeds ranging up to several hundred meters per second by means of a gun to impact the fluid and cause tensile stress cracks in the material by the established pressure. Such techniques are not amenable to non-vertical holes. Moreover, the rapidly moving piston presents a potential hazard to a user.
U.S. Pat. No. 3,507,540 issued to Silverman on Apr. 21, 1970 uses an expandable packer filled with pressurized hydraulic fluid. A circular channel or kerf is drilled and possibly a central hole drilled as well. The packer is inserted into the bottom of the central hole and the fluid pressure increased until the core fractures. Alternatively, a pair of packers may be inserted into the circular channel at diametrically opposite locations and the pressure then increased until fracturing occurs. The Silverman method requires pumps, a tank and piping leading to and from the pump to the packer. In addition, there is a limit as to the forces the walls of the packer can withstand without rupturing.
Accordingly, it is an object of the invention to provide an improved method of and apparatus for fracturing rock. It is a further object of the invention to provide a method of fracturing and removing large pieces of rock or other similar materials. It is yet another object of the invention to provide a method of fracturing rock which is simpler, more reliable and less expensive than predecessor methods.